In, for example, the radar art it is frequently necessary to sample the frequency of the individual pulses in an incoming pulse train to the receiver. This can cause problems, especially, when every incoming pulse has a very short duration and particularly when the carrier frequency varies from one pulse to another. The incoming signal consists, for example, of pulses having mutually different frequency values, which for example, constitutes the signal from different radar stations. The device should after the sampling deliver a signal with the same frequency as the received carrier. Examples of known circuits or systems for this purpuse is described in, for example, the U.S. Pat. No. 3,996,588.